 struct ListNode {
    int val;
    struct ListNode *next;
  };
 
typedef struct ListNode ListNode;
struct ListNode* middleNode(struct ListNode* head) {
    ListNode* slow = head;
    ListNode* fast = head;
    while (fast && fast->next)
    {
        slow = slow->next;
        fast = fast->next->next;
    }
    return slow;
}